The difference between training with discord and without is huge. I've trained a couple dozen cu sidhe to sell and the last one is the first that I used discord on.
Without discord using rottens, my dog would gain 0.1-0.2 healing per hour, and of course promptly die on me and lose that.
With discord and fighting thing she could survive (I didn't notice any differences in gains while poisoned), went from 90.0 to 98.5 in 4 hours. It still takes a long time.